This invention concerns portable transmitters for wireless remote control systems, especially those for controlling operations of a plurality of television receiver functions, such as on-off, volume and channel change. Specifically the invention is directed to remote control systems employing an electronic generating apparatus for producing electrical signals which are thereafter converted to acoustical signals via the mechanism of an electroacoustic transducer.
The transmitter of the related application mentioned above incorporates a two transistor oscillator arrangement which is frequency controlled by resistive elements and single-pole, momentary contact switches. The output of the oscillator is supplied to an output transistor circuit which drives a tuned electroacoustic transducer. While the instant invention performs the same functions and indeed utilizes similar switches, output transducer and single resistors for controlling the output signal frequencies, the oscillator mechanism is different and the inventions are distinct.
The transmitter apparatus in the above-mentioned application comprises a printed circuit supporting discrete resistors, transistors, capacitors and coils for producing the appropriate control frequencies. In contrast, the apparatus of the present invention has an active thick film circuit which includes all components except the battery, bypass capacitor, switch assembly, transducer and tuning coil. In particular a well-known pulse producing integrated circuit chip is made a part of the active thick film circuit. The result is a readily manufacturable, economical, stable circuit element which may be conveniently used in a portable signal transmitter.
The advantages obtainable with thick film processing contribute to the attractiveness of the invention. For example, the individual frequency determining resistors (used to change the time constant for the pulse producing circuit) may be laser trimmed with speed and precision. In practice the resistors are trimmed on the substrate (before encapsulation) while the output electrical frequency is being measured. Thus, rather than specifying close tolerances on parts, or trimming the resistor to specific values, they are trimmed until the desired frequencies are obtained. The process is readily automated and contributes greatly to the advantages realized by the inventive combination.